Stabilizing hydrogen peroxide solutions with pyrophosphoric acid



oxide solutions,

Patented Jan. 1 4 1936 UNITED. "STATES PATENT canes I STABILIZING HYDROGEN PEBOXIDE SOLU- TIONS WITH PYROPHOSPHOBIC ACID Joseph s. Reichert, Niagara Falls, N. Y., aslignor to E. I. du Pont deNemours & Company, Inc., Wilmington, DeL, a corporation or Delaware No Drawing.

Application September 12, ,1932, Serial No. 632,796

8 Claims. (01. 23-251) This invention relates to the stabilization of hydrogen peroxide solutions and more s'pe'cifi-. callyto the stabilization of the high concentration acid hydrogen peroxide monly transported.

In general it should be stated that hydrogen peroxide solutions are of two kinds, the first those which are transported and which are usually of relatively high concentrations, e. g. 10- volunie or stronger, and which have been acidified in order to have maximum stability, and

solution as comsecondly, the more dilute, alkaline hydrogen peras are commonly used .for

ever, are more stable than the alkaline solutions and it is therefore preferred that for transportation and storage purposes the solutions be of an acid character. However, merely acidifying the-peroxide with a mineral acid does not impart suificient stability for transportation and storage purposes. Certain additional stabilizers have been proposed for such acid, relatively highconcentration, peroxide solutions but they. have been ofan unsatisfactory nature for several reasons. Many organic stabilizers arevery effective in retarding the decomposition of impure hydro-'- gen peroxide and their use adds very little to the peroxide production costs. However, organic stabilizers have undesirable properties. Mate- V rials such as salicylic acid or acetanilide form colored solutions if there are traces of iron salts in the bleach-bath in which the peroxide is subsequentlyused, or the peroxide solution itself may become colored, due to the oxidation of these organic stabilizers. Furthermore, organic stabilizers are decomposed if the concentrated peroxide solutions are heated or allowed to stand for long periods and thereby lose their stabilizing properties.

Inorganic stabilizers are, in general, not as effective as organic stabilizers. The solubility of many inorganic compounds-in strong acid peroxide solutions is small so that either cloudy solutions are obtained, or it is impossible to introduce enough stabilizer. Many inorganic materials as for example, ferric chloride, cause acid peroxide solutions to decompose rapidly.

The object of this invention is to provide a stabilizer for acidifled hydrogen peroxide solu-' tions and more particularly for a hydrogen peroxidesolution or a concentration as ordinarily 'None shipped in commerce, i. e. about iii-volume or higher, and to provide a high concentration per-- oxide solution which can be shipped and stored for relatively long periods without serious losses.

' I have discovered that pyrophosphoric acid is an excellent stabilizer for hydrogen peroxide solutions of the nature described above. By stabil-- 'izing hydrogen peroxide solutions with pyropros phoric acid, the combined stabilizing effect of a the hydrogen ion and the pyrophosphate ion is 10 obtained. Hydrogen peroxide solutions stabilized with pyrophosphoric acid show only very small losses when stored for long periods of time even at temperatures higher than the normal storage temperature.

In carrying out the present invention, a small amount, for example, 0.025 to 1.5 grams or more of pyrophosphoric acid is dissolved per liter of hydrogen peroxide solution to be stabilized. If

the peroxide solution is not at the'bptimu'm acidity for stabilization, the pH is adjusted to the proper value by' acids or alkalies as required. The results thereby obtained are shown in the following examples:

Example I I To portions of freshly prepared commercial hydrogen peroxide solution of 100-volume strength, varying amounts of pyrophosphoric acid were added. The acidity of the peroxide was adjusted after adding the pyrophosphoric acid to a pH of about 2.

These portions were stored at a constant temperature of 32 C. for a period of three months, together with other portions containing no stabilizer. During this time, at intervals of 30 days, the solutions were analyzed to determine the loss in volume concentration. The results appear in the followingi'table:

Volume loss during storage at 32 0.

Concentration 01 H PiO1 30 days 60 days days 0.7 gram per liter--- 1.6 grams per liter mooscncnoo These results indicate that pyrophosphoric acid added in small amounts has a marked stabilizing to effect on acid hydrogen peroxide solutions,'and also that additions of 0.7 gram per literor more tend to produce low losses for periods of over 2 months at 32 C.

Example II 55 To portions of freshly prepared commercial hydrogen peroxide solution of loo-volume strength an equivalent to 0.4 gram per liter of pyrophosphoric acid as NMPaOvJOI-IzO was added. The 50 pH was adjusted to 4.3 after the addition of the NMPiO'LlOHQO.

This portion and a portion of unstabilized hydrogen peromde were stored at a temperature of 32 C. for 30' days. At the end of this storage period both samples were analyzed for the loss in volume concentration. The results appear in the following table:

- Volume loss Concentration 0! mac 3 at 323i for 60 days None 75. 7 0.04 gram per liter.... 7

The results of this experiment show the efiectlveness of small amounts of EJ412201 as a stabilizer 0 for hydrogen peroxide solutions.

Example HI To samples of 50-volume impure grade hydrogen peroxide, sodium pyrophosphate equivalent to 0.5 gram per literwas addedand the solution-adjusted to a pH of 5 with H2804 or NaOH. Other samples of the same peroxide containing no stabilizer were adjusted to a pH or 5 and tested with the stabilized samples. All samples were maintained at a constant temperature of 32 C. and

the rate of oxygen evolution was measured. From these measurements the losses in volume concentration equivalent to the loss over a period of 30 days were calculated. These results appear in the following table:

E uivalent v 30 y, 32 0. Concentration of NMPBOLIOHEO volume concentraticn loss None 19. 3 0.6 gram per liter (equivalent to 0.2 grams 114F10 5. 6

results indicate that HePzOr produced by adding NMPzOw to an acid hydrogen peroxide sc lution, is an eifectlve stabilizer in impure grades oi peroxide solutions.

- gen ion concentration on the eflectiveness of my mample IV illustrates the influence of hydrostabilizer.

Erample IV A series of ltd-volume hydrogen peroxide solutions having varying degrees of acidity were prepared and 0.66 gram per liter oi pyrophosphoricv acid was diwolved in a. portion of each solution.

These solutions were tested as in Example III with the following results:

. Equivalent to o oncentmtion ra ion concentration (9!!) mm loss stabilized 1.! as 0.2 l 0. 8 0- 4 3 B. 6 0. l 4 it. 0 0. as 4 84. 0 0. 76 5 Not tasted. o. s a Not tested. 2. 6 7 Not tested 6. 6

i A convenient method of, the pyrophos phoric acid is by heating orthophosphoric acid to a loss in weight of about 20%.-

The stabilizing action of pymphosphoric -acid maythusbesecuredbyaddingtothehydrogen peroxide solution a salt of the acid, for example,

alkali metal pyrophosphate or alkali metal acid pyropho sphates, together with suficient of a strong acid to acidity the solution, or, p ophosphoric acid itself may be added to the acid solution.

posed to stabilize bleach liquors over'a pH range or 7-10 with an alkali pyrophosphate. Here,

I however, the beneficial effector pyrophosphoric acid is not secured because care is taken to maintain the solution within the definitely alkaline pH'range of 7-10. Thus, the stabilizer is not pyof my Pyrophosphoric acid stabilizer is due to pyrophosphate ions in the presence of hydrogen .ions, and, further, that alkali metal ions which are undoubtedly present in, for example, hydrogenperoxide solutions of pH 5 have no stabilizing action on hydrogen peroxide solutions. Thus, the efiectiveness of this stabilizer can only be I am awarethat it has been previously pro- 1 secured in solutions which are acid,'i. e. have a pHof less than 7.

I have found pyrophosphoric acid to be of special utility in stabilizing hydrogen peroxide solutions for storage purposes at ordinary temperatures. I find it of considerable utility when used in combination with other stabilizers which also have a specific effect in stabilizing hydrogen peroxide at relatively high temperatures.

The exact amountof pyro'phosphoric acid needed to secure maximum stability will vary over a wide range dependent on several factors such as impurities in the peroxide and other dissolved matter. I have used as little as 0.025 gram per liter and up to 1.5 grams per liter,'but

do not wish to be limited in the amount to be added because of the variations found.-

Asshownin the foregoing, the efiectiveness of pyrophosphoric acid as a stabilizer exists in acid solutions, and in general, the best results are secured with pyrophosphoric acid alone when the stability 01 the solution lies'in the pH range of about 1.5-4.5. However, I have found pyrophosphoric acid alone effectively stabilizes hydrogen peroxide solutions over the pH range between 1 and substantial neutrality. Hence, in this specification, and in the appended claims, when the pH is defined as being between 1 and 7. it means up to but not including 7. While the most eflective range for pyrophosphoric acid alone isv between about 1.5 and 4.5, when pyrophosphoric acid is used in combination-with other stabilizers, the most efi'ective pH range 7 may be altered. Thus, with solutions 01' tin compounds as disclosed and claimed in m co-pendin: application, 8. N. 572,721, filed Nov. 2, 1931, Patent'No. 1,958,204, May 8, 1934, the most eflective pH range is between about 3.5 and 6. Fur--v .thermore, the most suitable pH of the peroxide solutions and. the exact amount oi pyrophosphoric acid to be used for any specified lot of peroxide solutions must be adjusted in accordance with other variables such as impurities present in peroxide solutions the nature of storage gment W and the storage What is claimed n,

I 1. A method oi stabilizing a hydrogen peroxide solution which comprises adding thereto a stacondibiliaerwhich consists of a small amount of a' tion a stabilizer which consists of pyrophosphoric acid in amountsranging from 0.025 gram to 1.5

grams per liter of solution, and then adjusting the acidity of said solution to a pH value of between 1 and 'I.

4. A method oi preparing a stable, low residue,

I 100 volume solution of hydrogen peroxide which comprises the steps of adding to the hydrogen peroxide solution a stabilizer which consists of pyrophosphoric acid in an amount ranging from Patent No.2,o27,sss.

numbered patent requiring corr mclusive, under Example IV, s the following:

.i'rom 0.025 gram to 1.5

' Certificate of Correction JOSEPH s. REIOHERT 0.025 gram to1.5 grams per liter of solution. and

thenadjusting the acidity of said solution to a pH value of between 1 and '1.

5. A process (or preparing a stable solution of hydrogen peroxide which comprises the steps of adding to the hydrogen peroxide solution a stabilizer which consists of a pyrophosphate in an amount chemically equivalent to 1rom-0.025 gram to 1.5 grams or pyr'ophosphoric acid per liter, and then adjusting the acidity of the solu- 10 tion to a pH value of between 1.5 and 4.5.

6. A homogeneous, stable solution 01' hydrogen peroxide of an acidity equivalent to a pI-I'value oi less than 6. which contains as a stabilizer a small amount 01' pyrophosphoric acid.

7. VA homogeneous, stable solution 01 hydrogen peroxide of an acidity equivalent to a pH value of between 1 and 7 which contains, as a stabilizer, pyrophosphoric acid in an amount ranging per liter.

8. .A homogeneous, stable solution of hydrogen peroxide of an'acidity equivalent to a pH value of between 1.5 and 4.5 which contains as a stabilizer pyrophosphoric acid in an amount ranging $5 from 0.25 gram to 1.5 grams per liter.

' .rosrren s. mom'r.

nts, 14, 1936.

It is hereby certified that error appears in the printed specification of the above ection as follows: Page 2, first column, lines 59 to 63, trike out the heading tothe table and insert instead Equivalent 30 Day Volume Concentration Loss Hydrogen Ion Concentration (pH) Stabilized Solutions and that the said Letters Patent should be read withthis correction therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealedthis 25th day of February, A. D. 1936.

[snarl] a LESLIE FRAZER, Acting Commissioner of Patents.

Certificate of Correction 1 Patent No. 2,027,838. January i4, 1936.

JOSEPH s. REICHERT It is hereby certified thaterror appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, lines 59 to 63, inclusive, under Example IV, strike out the heading tothe table and insert msteed the following:

Equlvnlent 30 Day Volume Concentration Lom Hydrogen Ion Concentration (pH) 7 Unstablllzed Solutions Stabilized Solutions and that the said Letters Patent should be read with this correction therein that the same rnay conform to the record of the case in the Patent Oflice.

Slgned and sealed this 25th day of February, A. D. 1936.

. LESLIE FRAZER, Acting Commissioner of Patents. 

